SA Senator Simon Birmingham and Premier Jay Weatherill are engaged in a war of words over the State Government's failure to give evidence at a Senate inquiry into Murray-Darling Basin reform in Adelaide this morning.

The hearing, to discuss legislation relating to last month's announcement of a $1.8 billion fund to secure up to 450 billion litres of extra water for the river, was attended by various environmental groups, as well as the Victorian Farmer's Federation and a Victorian wine grower's group.

The State Government declined an invitation to attend, instead pledging to provide a written submission.

Representatives from the Australian Conservation Foundation, Wilderness Society and Conservation Council SA told the inquiry the fund was unlikely to deliver the outcomes acclaimed by Mr Weatherill and Prime Minister Julia Gillard.

Senator Birmingham, the opposition's Basin spokesman, seized on the non-attendance, accusing Mr Weatherill and the State Government of failing to explain why the legislation did not match "the hype".

"They were clearly invited to be here and they turned it down," he said.

"Two weeks ago Jay Weatherill was happy to stand alongside Julia Gillard and sing what a great result this was for the Murray-Darling.

"Today we've heard from numerous environmental organisations that they don't believe what is before us in term of Legislation delivers on what was promised by Jay Weatherill and Julia Gillard.

"So he should be coming out, the South Australia Government should be coming out, and explaining why it is that the reality isn't matching Jay Weatherill's rhetoric."

Mr Weatherill told a press conference the time for talking was over and the inquiry was merely a distraction.

The government was invited to attend on Tuesday.

"This is just a distraction that the Liberal senators will do anything to avoid answering the simple question whether they support the 3200 gigalitre plan to restore this river to health. That's what this is all about. The time for talking is over the time for action is now here."

The inquiry is chaired by Labor Senator Doug Cameron and includes three coalition members, as well as Independent Senator Nick Xenophon and Greens Senator Larissa Waters, who was not present.

Senator Xenophon, who intends to move several amendments to the legislation, including ensuring the wording called for `at least' 450 gigalitres rather than `up to', said Mr Weatherill's assessment of the inquiry was wrong.

"If the Victorian Farmer's Federation could turn up you'd think the SA Government could have," he said.

Mr Birmingham also took to social media to bait Mr Weatherill, tweeting: "why did @JayWeatherill fail to turn up & argue for Murray-Darling Basin Plan legislation?"

He told reporters the State Government's absence was baffling.

"You would have thought the opportunity to try to sell to a Federal Senate inquiry, involving senators from NSW and Victoria, South Australia's position would have been too good an opportunity to refuse."